There is a class of tobacco smoke filter which utilizes a differential in the kinetic energy of smoke and of liquid and semi-liquids entrained in the smoke to separate and then trap the liquid and semi-liquid constituents. Many of the filters which rely on that principal are very effective in removing tars and nicotine. But, design has been a matter of art rather than a science, and most design approaches have failed.
The most successful approach appears to have originated with Lebert and can be traced through the work of Thomas and the work of Aikman. Lebert, U.S. Pat. No. 2,954,772 put a barrier across the flowpath of a cigarette holder, a smoke accelerating hole through the middle of the barrier, and a second barrier downstream in the path of smoke passing through the accelerating opening. The smoke and entrained liquids and semi-liquid particles were accelerated toward the second barrier when the smoker applied suction pressure by inhaling. In that process the entrained particles acquired kinetic energy more than did the smoke. The smoke flowed around the second barrier, but the entrained particles could not. They impinged and collected on the face of the second barrier.
The Lebert filter was technically, but not commercially, successful. Thomas made a more commercial product by adding an ambient air inlet upstream from the first barrier. His patents, U.S. Pat. Nos. 3,810,476, 3,926,199 and 3,548,835, also reveal an attempt to move the collection of entrained liquids and semi-solids away from the face of the second barrier to avoid the buildup of trapped matter in front of the accelerating opening. He converted the opening to a lateral passage which opened opposite the inside wall of the downstream chamber whereby collection occured over a broader area.
Aikman, as shown in U.S. Pat. No. 4,038,904, adopted the kinetic energy differential separation principle of Lebert and the air inlet of Thomas. He succeeded in accomplishing adequate separation in regions downstream from the second barrier.
What characterizes the work of all three of these prior inventors is that their filters had to be arranged in relatively long structures. Lebert and Thomas put their filters inside conventionally shaped cigarette holders. Aikman modified the external appearance somewhat, but all three made cigarette holders with filter elements inside. The cost of such structures was too great to be treated as throw-away units. They had to be made in a way that permitted disassembly for cleaning or replacement of the filter element. No one could successfully remove the second barrier and, as a consequence, one-piece, throw-away construction was not possible.
The addition of the ambient air inlet converted the filter-in-a-cigarette-holder device to one that was an aid to those users who wanted to withdraw from the smoking habit, and sets of filter holders, each with a different sized ambient air inlet, became known as "smokers' withdrawal kits." Holders were used over and over. They had to be cleaned and preserved and, ultimately for most smokers who used them, their use simply became part of the smoking habit rather than a means to quitting smoking. The industry looked for, but failed to find, what was predicted to be a better aid to quitting, or at least a less expensive way to filter out of the smoke a large share of the tars and nicotine products. It failed to find a one-piece disposable filter.
Building the filter inside the cigarette itself proved not to be the answer. The best technology for withdrawal filters requires the provision of ambient air for condensing out the liquids containing tar and nicotine and to collect the condensed materials in a fashion that insures against their reentry into the smoke stream. The makers of cigarettes are not motivated to adopt filtration of the kind that aids in overcoming the smoking habit.
The purpose of this invention is to apply the best filtration technology, the technology which can aid some smokers to give up smoking, in a very low cost unit which can be considered to be disposable.